Numerical simulation of a mechanical flocculation process with multi-chambers in series

A mechanical flocculation system with multi-chambers in series is commonly used as the advanced phosphorus removal technology for wastewater treatment. This work aims to numerically investigate the inner states and overall performance of industrial-scale mechanical flocculators in series. This is based on our previously developed computational fluid dynamics (CFD) flocculation model which is extended to consider the key chemical reactions of phosphorus removal. The effects of the number of flocculation chambers, locations, and sizes of the flocculation chamber connection as well as operational combinations of impeller speeds are investigated. With a decreasing number of flocculation chambers, the main vortexes and chemical reactions are weakened, while the small flocs form. Both the phosphorus removal efficiency η and the average floc size d_p reduce as the number of flocculation chambers decreases. The connection location of flocculation chambers directly determines the turbulent flow, thus influencing the key performance indicators. However, the phosphorus removal efficiency η and average particle size d_p are little affected by the size of the flocculation chamber connection. As the impeller speeds in series gradually increase, the gradient of floc size distribution in each chamber is enlarged and the chemical reaction is enhanced over the working volume.

Flocculation kinetics of low-turbidity raw water and the irreversible floc breakup process

The main objective of this study was to propose an improvement to the flocculation kinetics model presented by Argaman and Kaufman, by including a new term that accounts for the irreversible floc breakup process. Both models were fitted to the experimental results obtained with flocculation kinetics assays of low turbidity raw water containing Microcystis aeruginosa cells. Aluminum sulfate and ferric chloride were used as coagulants, and three distinct average velocity gradient (G) values were applied in the flocculation stage (20, 40 and 60 s^-1). Experimental results suggest that the equilibrium between the aggregation and breakup process, as depicted by Argaman and Kaufman's original model, might not be constant over time, since the residual turbidity increased in various assays (phenomenon that was attributed to the irreversible floc breakup process). In the aluminum sulfate assays, the residual turbidity increase was visible when G = 20 s^-1 (dosages of 60 and 80 mg L^-1). For the ferric chloride assays, the phenomenon was noticed when G = 60 s^-1 (dosages of 60 and 80 mg L^-1). The proposed model presented a better fit to the experimental results, especially at higher coagulant dosages and/or higher values of average velocity gradient (G).

Assessing the effect of flow fields on flocculation of kaolin suspension using microbial flocculant GA1

CFD simulations were employed to assess the effect of flow fields on flocculation of kaolin suspension using microbial flocculant GA1.